I'd like to suggest the option to disable align merge sources for the Focus Merge tool. Some modern cameras, such as the Fujifilm X-T4, have in-camera focus bracketing and all my images come out aligned (unless, of course, some outside force moves the camera or subject).
I primarily use Helicon Focus and when I have align sources enabled then it, too, takes a very long time. Affinity Photo is taking somewhere between 25-30 minutes for 73 photos. This is rather long considering some stacks are close to 200 images. Helicon Focus was able to stack the same images in about 5 minutes. I understand that Affinity Photo isn't primarily an image stacking application, as is Helicon Focus, but 20-30 minutes is a bit too long and, I feel, the aligning of the photos is partly to blame.